The invention claimed and disclosed herein pertains to heat pumps, and more particularly to methods and apparatus to improve the efficiency of an evaporator in a heat pump.
A heat pump can be a useful apparatus for heating or cooling an indoor environmental space, such as a home or an office building. The great majority of heat pumps work on an air-to-air-basis. That is, the heat pump moves thermal energy from one mass of air to another mass of air. The two masses of air typically are air in the indoor environmental space, and outdoor atmospheric air. In essence, the heat pump is configured as a reversible refrigeration unit. That is, the heat pump can be operated so as to cool the indoor environmental air, or it can be operated to cool the outdoor environmental air (in which case the thermal energy from the outdoor atmospheric air is transferred to the indoor environmental space, thereby effectively heating the indoor air).
FIG. 1 depicts a prior art refrigeration system 1. This system can be considered as essentially xe2x80x9chalfxe2x80x9d of a heat pump. (A heat pump actually includes two thermal expansion valves versus just the one valve 4 depicted in the figure, as well as a reversing valve to reverse the direction of flow of refrigerant in the system. The simplified system 1 of FIG. 1 is shown for illustrative purposes only.) In FIG. 1, when the heat pump is operating to warm the indoor environmental space (and conversely cool the outdoor atmospheric air), the condenser 3 is located in the indoor space, and the evaporator is located in an outdoor environment. The system 1 circulates a refrigerant in a closed loop, as indicated by the flow direction arrows in the figure. Refrigerant in a vapor form is discharged from the compressor 2 (or xe2x80x9cKxe2x80x9d), and is directed to the condenser 3. As the refrigerant passes through the condenser, heat is extracted from the refrigerant by passing the indoor air over a series of coils through which the refrigerant passes. As heat QB is extracted from the refrigerant (and passed to the indoor environmental space), the refrigerant condenses from a vapor form to a liquid form. The liquid refrigerant then passes through a thermal expansion valve 4 where it flashes from a liquid to a vapor. The heat of vaporization causes a significant drop in the temperature of the refrigerant. The refrigerant is then passed through the evaporator 5, where it absorbs energy QB from the outdoor atmospheric air. The evaporator 5 comprises a series of tubing coils through which the refrigerant is passed. The refrigerant coils are typically in thermal energy communication with a series of heat transfer plates (or fins) which provide a larger surface area over which the heat transfer process can occur. The outdoor atmospheric air is forcibly moved over the heat transfer plates by a fan, and thus energy from the outdoor air is transferred to the refrigerant so that it can be subsequently transferred to the indoor air in the manner just described.
FIG. 2 depicts a typical installation for a heat pump evaporator. The setting is a residential house xe2x80x9cHxe2x80x9d. The heat pump evaporator 10 (also known as the outdoor heat exchanger) is typically located proximate to one side of the house. Refrigerant inlet and outlet lines 12 and 14 connect the heat pump evaporator to the other the components of the heat pump, which can be located in the house xe2x80x9cHxe2x80x9d. The heat pump is commonly supported by a slab or a platform 11. The evaporator 10 is provided with a fan 16 which causes air to be drawn in from the sides of the evaporator and exhausted from the top of the evaporator. As the air is drawn through the evaporator, it passes over heat transfer plates 18 in the manner described above.
It should be appreciated that when the heat pump is operating to heat the indoor air, the outdoor heat exchanger operates as an evaporator. However, when the heat pump is operated to cool the indoor air, then the outdoor heat exchanger operates as a condenser. Since the present invention pertains to a heat pump operating in a mode to heat indoor air, I will refer to the outdoor heat exchanger as an xe2x80x9cevaporatorxe2x80x9d.
Under the right conditions, a heat pump can be a very effective and efficient device for heating (and cooling) an indoor environmental space. However, in locations where the outdoor temperature can be very cold, or where the average temperature in winter months is relatively low, then the heat pump becomes less efficient since the thermal gradient between the refrigerant in the evaporator and the outdoor air can be low. That is, the higher the thermal gradient between the refrigerant in the evaporator and the outdoor air, the more effective the heat pump will be at heating the indoor space.
What is needed then is a heat pump which achieves the benefits to be derived from similar prior art devices, but which avoids the shortcomings and detriments individually associated therewith.
The present invention provides for methods and apparatus to increase the performance of an evaporator in a heat pump system when the heat pump system is being used to heat an indoor environmental space. The invention allows the performance of the heat pump evaporator to be increased by directing solar radiation to heat transfer plates within the evaporator. Generally, the evaporator is located in an outdoor environment.
A first embodiment of the present invention provides for a solar reflector for the evaporator described in the previous paragraph. The solar reflector includes a curved surface configured to reflect solar radiation to the heat transfer plates of the evaporator. The curved can be in the shape of a truncated parabola. That is, the curved surface is formed like a parabolic dish, but the bottom of the dish is xe2x80x9ccut offxe2x80x9d. This results in an opening in the curved surface which can accommodate the evaporator so that the curved surface can be placed around the evaporator by lowering it over the evaporator from the top. Further, the curved surface can be a dish-like shape (not necessarily parabolic) such that the curved surface defines an upper perimeter and a lower perimeter. The lower perimeter then defines a bottom opening which accommodate the evaporator. In this way the solar reflector can be placed around (at least part of) the evaporator to focus reflected solar radiation towards the heat transfer surfaces of the evaporator. This solar radiation warms the heat transfer surfaces, thus providing more energy which can be used to heat the indoor environmental space.
Since the evaporator can be provided with a refrigerant supply line and a refrigerant return line (as well as an electrical power line), these service lines can interfere with a solar reflector which is configured to completely surround the evaporator. Accordingly, the upper and lower perimeters of the curved surface can be configured to each form a partial circle, rather than a full circle. The xe2x80x9cgapsxe2x80x9d in each of the perimeters can then be aligned to thusly define a gap in the curved surface. The gap can then receive one of more of the service lines to allow the curved surface to be fit around the evaporator.
Also, in some instances the evaporator is located close to a building or a structure, and so it is not possible to completely surround the evaporator with a dish-type solar reflector. In this case the upper perimeter of the solar reflector can form a partial circle, and the lower perimeter can define three sides of a rectangular opening (or a partial circular opening). The rectangular opening (or the partial circular opening) is configured to receive the evaporator. In this case, rather than drop the solar reflector over the evaporator from the top, the solar reflector can be xe2x80x9cslidxe2x80x9d into place from the side of the evaporator.
To further improve the performance of the solar reflector, the inner surface (i.e., the surface facing the evaporator) of the curved surface can be a highly reflective surface. For example, the curved surface can be fabricated from metal (such as stainless steel or aluminum), and the inner surface can then be polished to improve the solar reflecting (and focusing) properties of the solar reflector.
Since the solar reflector can be used for existing installations of evaporators, it is desirable to allow the solar reflector to be adjustable to that it can accommodate a variety of different sizes of evaporator. In one variation the solar reflector can have legs to support the curved surface on a horizontal support surface. These legs can be adjustable in height to allow the solar reflector to focus the reflected solar radiation directly on the heat transfer plates in the evaporator.
A second embodiment of the present invention also addresses the issue of allowing the solar reflector to be adjustable to accommodate different configurations of evaporators. In this embodiment the solar reflector comprises a plurality of partially overlapping curved surfaces. Each curved surface is configured to reflect solar radiation to the heat transfer plates of the evaporator. The solar reflector also includes a hinge ring to which each of the curved surfaces are hingedly attached. The hinge ring can define an opening configured to receive the evaporator. Thus, when one curved surface is rotated about the hinge ring, all of the other overlapping surfaces will follow, allowing the curved surface to be spread out or pulled closer together. In this way the curved surface can be adjusted to more effectively focus the reflected solar radiation on the heat transfer plates (surfaces) of the evaporator. In order to hold the curves surfaces into a fixed position once they have been moved to a desired position, a clip can be used to secure the outside edges of two adjacent overlapping curved surfaces to one another.
In order to address the issue of service lines which can make it difficult to place a continuous curved surface around the evaporator, or where the evaporator is located close to a structure so that a full continuous dish shape can be used, one or more of the adjacent curved panels can be eliminated to leave a xe2x80x9cgapxe2x80x9d in the collective surface for the service lines. Also, the hinge ring can be an open ring (i.e., a ring with a gap in the defining structure), allowing the solar reflector to be xe2x80x9cslidxe2x80x9d into place.
A third embodiment of the present invention provides for a modified evaporator in a heat pump system. The evaporator has a curved, reflective surface configured to reflect solar radiation to heat transfer plates in the evaporator. The evaporator can be defined by an outer perimeter, and further the curved surface can be configured to fit around the evaporator in proximity to the outer perimeter. Further, the evaporator outer perimeter and the curved surface can define a gap there between. This gap can allow rain and melting snow, and small debris, to pass between the curved surface and the evaporator, rather than allowing it to accumulate in the bottom of the curved surface.
A fourth embodiment of the present invention provides a method for improving the performance of an evaporator in a heat pump. The evaporator has heat transfer plates, and is (preferably) located in an outdoor environment. The method includes the steps of focusing solar radiation, and directing the focused solar radiation at the heat transfer plates in the evaporator. This focusing and directing can be performed using the solar reflectors described above. Further, when the heat pump is used to heat the indoor space of an associated building having a plurality of sides, and a first side of the building is exposed to more direct solar radiation during the winter season than another side of the building, the method can include locating the evaporator proximate to the first side of the building. This places the evaporator in a location where solar radiation can more easily be focused and directed to the heat transfer plates.
These and other aspects and embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein: